As you may have guessed, these heads in the foreground of panels 1 and 3 (and the body in the background of panel 2) are cameos from another webcomic, specifically Grrl Power. What you might not have guessed (unless you're very observant about things like eye colour and skin tone) is that they are all the same cameo, specifically, the five bodies that comprise the character Harem.

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(Thursday morning, INT: gym, EB and MH are in the showers, naked. Various heads obscure all nudity.)

MH: Anyhoo, we're getting away from the key topic of discussion, here, which is the fact that you're totally sun-deer for Jamie. You're so sun-deer it hurts.
EB: It's pronounced tsoon-day-ray, and I'm totally not.
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MH: You wanna know how I know you're lying?
EB: Enlighten me.
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MH: You usually only shave your legs and pits once a week on Sunday. Here it is Thursday, and I see no stubble.
EB: I got a new razor recently, and had to try it out. Jamie's got nothing to do with it.
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MH: Also, you usually look like you're perpetually getting head from Jimi Hendrix.
EB: The razor slipped, and I had to even it out.
EB: ...quit looking at my crotch.